It has been proposed to monitor manufacturing equipment continuously. The documents FR-A-2 312 060 and FR-A-2 605 170 are examples of the techniques used. As indicated in many documents which deal with such monitoring of complex equipment, the aim is to be able to monitor the progressive wear of the equipment in order to be able to use the machine to its maximum capability and to avoid stoppage due to the breakage of a component or stoppage for preventive changing of a component still in a state of functioning. Wear is a relatively slow progressive phenomenon and monitoring can in general be provided by alternating scrutiny of the various sensors.
The invention proposes to use continuous monitoring of machines not only for detecting breakdowns but also to check the quality of production. It can therefore be seen that the aim is different. In fact, temporary random perturbations may occur on the equipment and cause transient phenomena which may impair the quality of the product manufactured.
In fact, it is well known that in equipment for manufacturing a photographic product, the noise vibration at the meniscus of the coating machine changes the thickness of the coating deposited with the frequency of the sound wave without impairing the operation of the equipment. A phenomenon of this type, when it appears temporarily, will not necessarily be detected by scrutiny by means of the various sensors. This is why, in the present description, it will be considered that the acquisition and processing are executed in "real time" when all the samples provided without interruption by an analog-to-digitial converter are processed and analysed, even if the results of the calculations are delivered with a certain perfectly calculatable delay or phase shift.
The document FR-A-2 605 170 describes the monitoring of complex equipment by the use of several sensors disposed at essential points in the equipment and the digital recording of the signals describing the phenomenon for the purpose of their subsequent processing by an analyzer. The monitoring proposed cannot therefore be considered to be monitoring in real time within the meaning of the present application.
The document FR-A-2 312 060 describes automatic monitoring apparatus in which the fundamental components of the equipment are monitored by a sensor associated with a channel. In this document it is mentioned that the analysis is carried out in real time. However, because of the architecture and mode of functioning of the monitoring apparatus, which automatically and successively selects each channel having a single analysis device, the processing of each sensor takes into account only a very limited portion of the signal and cannot be considered to be processing in real time as defined above. Moreover, the sensors are connected to the analysis unit by cables which may be as long as 150 m. Such lengths of cable in an industrial environment may cause distortions in the signal reaching the analyzer. Such distortions may result from the addition of noise or even significant stray signals.